net: dsa: remove name arg from slave create

Now that slave dsa_port always have their name set, there is no need to
pass it to dsa_slave_create() anymore. Remove this argument.

Signed-off-by: Vivien Didelot <vivien.didelot@savoirfairelinux.com>
Reviewed-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>